The amino acid sequence of the peptide containing the thiol group of creatine kinase from normal and dystrophic chicken breast muscle. Comparison of some of the immunological properties of the antibodies developed in rabbits against these enzymes.

The major (14)C-labelled peptides from creatine kinase from normal and dystrophic chicken muscle obtained by carboxymethylating the reactive thiol groups with iodo[2-(14)C]acetic acid and digestion with trypsin were purified by ion-exchange chromatography on Dowex-50 (X2) and by paper electrophoresis. The chromatographic characteristics of the (14)C-labelled peptides, their electrophoretic mobilities at pH6.5, and their amino acid compositions were identical for the two enzymes. The sequence of amino acids around the essential thiol groups of creatine kinase from normal and dystrophic chicken muscle was shown to be Ile-Leu-Thr-CmCys-Pro-Ser-Asn-Leu-Gly-Thr-Gly-Leu-Arg (CmCys, carboxymethylcysteine). This sequence is almost identical with that for the creatine kinases in human and ox muscle and bovine brain and is very similar to that of arginine kinase from lobster muscle. Antibodies to the enzymes were raised in rabbits and their reaction with the creatine kinase from normal and dystrophic muscles in interfacial, immunodiffusion and immunoelectrophoretic experiments was studied. The cross-reaction between normal muscle creatine kinase and antisera against the dystrophic muscle enzyme (or vice versa) observed by immunodiffusion and by immunoelectrophoretic experiments further suggests that the enzymes from normal and dystrophic chicken muscle are similar in structure. The results of the present study, the identical amino acid sequence of the peptides containing the reactive thiol group from both the normal and dystrophic chicken muscle enzymes and the immunological similarities of the two enzymes are in accord with the similarity of the two enzymes observed by Roy et al. (1970).